Amplifier circuit

Abstract

A current mirror amplifier (CMA) with controlled current gain, the current gain being changed, for example, responsive to the output condition of a comparator in which the CMA is used in a differential signal combining circuit. In such a comparator application the switched gain of the CMA imparts hysteresis to the comparator characteristics.

What is claimed is: 
     
       1. A current amplifier with controlled current gain comprising: input, output and common terminals;   a plurality of transistors of a first conductivity type, each having first and second electrodes with a controlled conduction path therebetween and having a control electrode, the conduction of the controlled conduction path of each transistor being controlled responsive to the potential between its second and control electrodes;   the first and second electrodes of the first of the plurality of transistors connected respectively to the input terminal and the common terminal;   the first electrode of the second of the plurality of transistors connected to the output terminal;   the first and second electrodes of the third of the plurality of transistors connected respectively to the second electrode of the second transistor and the common terminal;   direct-coupled feedback means between the first electrode of the first transistor and its control electrode to adjust the potential at the control electrode of the first transistor and condition the first transistor to conduct current, as applied to said input terminal, through its controlled conduction path;   means for applying a potential substantially equal to the potential at the control electrode of the first transistor to the control electrodes of the second and third transistors;   a source of gain-controlling signal;   a controlled impedance means connected between the common and output terminals; and   means for applying the gain-controlling signal to the controlled impedance means to vary, in accordance with the applied signal, the current gain of the amplifier within a range between a predetermined minimum current gain as defined by a ratio of the conductances of the first, second and third of the plurality of transistors and a predetermined maximum current gain as defined by the ratio of the conductances of first and second of the plurality of transistors.   
     
     
       2. A current amplifier as set forth in claim 1 wherein the controlled impedance includes: a fourth of the plurality of transistors, having its control electrode connected to the source of gain-controlling signal, the conduction of its path being controlled responsive to the potential between its second and control electrodes, its first and its second electrodes being connected respectively to the second electrode of the second transistor and to the common terminal.   
     
     
       3. A curent amplifier with controlled current gain as set forth in claim 2 connected in combination with the following elements to form a current comparator with hysteresis: means for applying the current to be compared to said input and said output terminals, respectively, of said current amplifier with controlled current gain,   a further transistor of the plurality of transistors having its second and control electrodes connected respectively to the common and output terminals of said current amplifier with controlled current gain; and   means for supplying quiescent current demand to the first electrode of said further transistor, the last-mentioned means exhibiting resistance across which said gain-controlling signal is developed.   
     
     
       4. A current amplifier with controlled current gain as set forth in claim 2 connected in combination with the following elements to form a voltage comparator with hysteresis: fifth and sixth transistors of the plurality of transistors, each having a second conductivity type complementary to said first conductivity type, each having first and second electrodes with a controlled conduction path therebetween and each having a control electrode, the conduction of its path being controlled responsive to the potential between its second and control electrodes, the first electrodes of said fifth and said sixth transistors being connected respectively to the input terminals and to the output terminals of said current amplifier with controlled current gain;   means for supplying current to an interconnection of the second electrodes of said fifth and said sixth transistors;   means for applying the voltage to be compared to the control electrodes of said fifth and said sixth transistors, respectively;   a seventh transistor of the plurality of transistors, of the first conductivity type, having its control and second terminals connected respectively to the output and common terminals of said current amplifier with controlled current gain; and   means for supplying quiescent current demand to the first electrode of said seventh transistor, said means exhibiting resistance across which said gain-controlling signal is developed.   
     
     
       5. A current amplifier, the current gain of which may be varied in response to a control signal comprising in combination: input, output and common terminals;   a source of control signal;   a first insulated gate field effect transistor (IGFET) having first and second electrodes defining a conduction path therebetween and a control electrode, the first electrode of the conduction path of said first transistor coupled to said common terminal and said second electrode coupled to said control electrode and said input terminal;   second and third IGFET's each having a control electrode and a conduction path, the control electrodes of said second and third IGFET's being connected to said input terminal and the conduction paths of said second and third IGFET's being serially connected between said output and said common terminals; and   switching means having a conduction path and a control electrode, said switch control electrode being connected to said control signal source and said switch conduction path being connected in parallel connection with the conduction path of one of said second and third IGFET's.   
     
     
       6. The combination as set forth in claim 5 wherein said switch means comprises a fourth IGFET having a control electrode comprising said switch control electrode and a conduction path comprising said switch conduction path. 
     
     
       7. A current amplifier with controlled current gain as set forth in claim 6 connected in combination with the following elements to form a voltage comparator with hysteresis: fifth and sixth IGFET's of a conductivity type complementary to conductivity type of the other IGFET's, each of the fifth and sixth IGFET's having first and second electrodes and a controlled conduction path therebetween and a control electrode, the conduction of each path being controlled responsive to the potential between its second and control electrodes, the first electrodes of the fifth and the sixth IGFET's being connected respectively to the input terminal and to the output terminal of the current amplifier with controlled current gain;   means for supplying current to the second electrodes of both the fifth and the sixth IGFET's;   means for applying voltages to be compared to the control electrodes of the fifth and the sixth IGFET's, respectively;   a seventh IGFET of the first conductivity type, having first and second electrodes and a controlled conduction path therebetween and a control electrode, the conduction of its path being controlled responsive to the potential between its second and control electrodes, the output and common terminals of the current amplifier with controlled current gain being connected respectively to the control and second electrodes of said seventh transistor; and   means for supplying quiescent current demand to the first electrode of the seventh transistor, the means exhibiting resistance across which the control signals are developed.   
     
     
       8. A current amplifier with controlled current gain as set forth in claim 6 connected in combination with the following elements to form a current comparator with hysteresis: means for applying the current to be compared to the input and the output terminals, respectively, of the current amplifier with controlled current gain,   a further transistor having first and second electrodes with a controlled conduction path therebetween and having a control electrode, the conduction of its path being controlled responsive to the potential between its second and control electrodes, the second and control electrodes connected respectively to the common and output terminals of the current amplifier with controlled current gain; and   means for supplying quiescent current demand to the first electrode of the further transistor, the last-mentioned means exhibiting resistance across which said gain-controlling signal is developed.   
     
     
       9. The combination set forth in claim 5 further including a series transistor of said first conductivity type having first and second electrodes defining a conduction path therebetween and a control electrode, the control electrode of said first and series transistors being interconnected, the first and second electrodes of said series transistor being connected to the first electrode of said first transistor and said common terminal respectively. 
     
     
       10. A current amplifier with controlled current gain as set forth in claim 8 connected in combination with the following elements to form a voltage comparator with hysteresis: fifth and sixth IGFET'T of a conductivity type complementary to conductivity type of the other IGFET's, each of the fifth and sixth IGFET's having first and second electrodes and a controlled conduction path therebetween and having a control electrode, the conduction of each path being controlled responsive to the potential between its second and control electrodes, the first electrodes of the fifth and the sixth IGFET's being connected respectively to the inut terminal and to the output terminal of the current amplifier with controlled current gain;   means for supplying current to the second electrodes of both the fifth and the sixth IGFET's;   means for applying the voltages to be compared to the control electrodes of the fifth and the sixth IGFET's, respectively;   a seventh IGFET of the first conductivity type, having first and second electrodes and a controlled conduction path therebetween and having a control electrode, the conduction of its path being controlled responsive to the potential between its second and control electrodes, the output and common terminals of the current amplifier with controlled current gain being connected respectively to the control and second electrodes of said seventh transistor; and   means for supplying quiescent current demand to the first electrode of the seventh transistor, the means exhibiting resistance across which the control signals are developed.   
     
     
       11. A current amplifier with controlled current gain as set forth in claim 9 connected in combination with the following elements to form a current comparator with hysteresis: means for applying the current to be compared to the input and the output terminals, respectively, of the current amplifier with controlled current gain,   a further transistor having first and second electrodes with a controlled conduction path therebetween and having a control electrode, the conduction of its path being controlled responsive to the potential between its second and control electrodes, the second and control electrodes connected respectively to the common and output terminals of the current amplifier with controlled current gain; and   means for supplying quiescent current demand to the first electrode of the further transistor, the last-mentioned means exhibiting resistance across which the gain-controlling signal is developed.